There are a number of contexts in which power and/or current stabilization and unbalance compensation are desirable to mitigate the inefficiencies and potential damage that can result from fluctuating energy demands. For example, in the case of alternating current (AC) electric arc furnaces, high power arcs are used to melt or smelt ore, metals and/or other materials, and these high power arcs behave as non-linear time varying impedances. The active or reactive power consumed by an electric arc furnace tends to fluctuate due to frequently changing operating conditions, causing frequency and/or voltage disturbances which may negatively impact the power supply and other loads connected to the same power supply.
In addition, electric arc furnaces tend to be connected as three-phase loads and may draw unbalanced currents from the power supply, which can lead to voltage imbalances. The resulting current imbalance may exceed the unbalanced current capacity of the supply system.
Loss of arc between the electrode and the furnace bath causes severe fluctuations in power and current drawn by the furnace from the power supply. Such loss of arc may result from, for example, the sudden input of new feed material into the furnace. In the case of smelting furnaces, new feed material is frequently added to the furnace while the furnace is in operation and is typically deposited around the area where electrodes are arcing. The new feed material typically has a relatively high electrical resistance, and the material cannot always be distributed evenly. Unevenly distributed feed material can push high resistance material under one or more electrodes, causing the resistance of the arcing path to be increased significantly, which may lead to extinguishment of the arc.
Arc losses cause furnace power and current drops. In a 3-phase, 3-electrode arc furnace, for example, a loss of arc under one electrode causes a 50% drop in furnace power. As a result, the furnace operator or the automatic electrode regulation system may have to lower one or more of the electrodes to establish contact with low resistance material in the furnace and slowly raise the electrodes in order to return the electrodes to their normal operating positions.
Arc losses usually do not occur under all electrodes at the same time. As a result of an arc loss, furnace currents may become severely unbalanced. This unbalance affects operation of the power generator and other loads coupled to the generator. In some circumstances, the power and current disturbances resulting from arc loss may lead to shutdown of power to the furnace, and possibly even shutdown of the generator. If the furnace or generator is shut down, there may be significant delays before it can be restarted, resulting in reduced operating efficiency and substantial economic loss.
It is desired to address or ameliorate one or more of the problems described above, or to at least provide a useful alternative to previous systems or methods.